CEMENT CONCRETE MIX DESIGN

byby

Patil Hitesh S

Assistant Professor SIEM Nashik .

Patil Hitesh S

IS-10262-2009

Concrete Mix DesignThe following points should be remembered before proportioning

a concrete mix a per IS-10262-2009.

• This method of concrete mix proportioning is applicable only

for ordinary and standard concrete grades.for ordinary and standard concrete grades.

• The air content in concrete is considered as nil.

• The proportioning is carried out to achieve specified

characteristic compressive strength at specified age,

workability of fresh concrete and durability requirements.

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Step-1. Design Specifications• Grade designation (whether M10, M15, M20 etc)

• Type of cement to be used

• Maximum nominal size of aggregates

• Minimum & maximum cement content

• Maximum water-cement ratio

• Workability

• Exposure conditions (As per IS-456-Table-4)

• Maximum temperature of concrete at the time of placing

• Method of transporting & placing

• Early age strength requirement (if any)

• Type of aggregate (angular, sub angular, rounded etc)

• Type of admixture to be used (if any)Patil Hitesh S

Step-2. Testing of Materials

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Step-3. Target Strength CalculationCalculate the target compressive strength of concrete using the formula given

below.

Where,

fck ’ = Target compressive strength

at 28 days in N/mm2 .

fck ’ = fck + 1.65s

at 28 days in N/mm2 .

fck = Characteristic compressive strength

at 28 days in N/mm2 .

s = Standard deviation

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Step-4. Selection of Water-Cement Ratio

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Minimum Cement content Maximum Water-Cement ratio andMinimum Grade of Concrete for different exposures withnormal weight of aggregate of 20mm nominal maximum size.

Sl.

No.

Exposure

Plain Concrete Reinforced Concrete

Minimum

Cement Content kg/m3

Maximum

Free Water Cement

Ratio

Minimum

Grade of Concrete

Minimum

Cement Content kg/m3

Maximum

Free Water Cement

Ratio

Minimum

Grade of Concrete

i) Mild 220 0.60 - 300 0.55 M20

ii) Moderate 240 0.60 M15 300 0.50 M25

iii) Severe 250 0.50 M20 320 0.45 M30

iv) Very

Severe

260 0.45 M20 340 0.45 M35

v) Extreme 280 0.40 M25 360 0.40 M40

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Sl.

No.

Environment Exposure Conditions

1 2 3

i) MildConcrete surfaces protected

against weather or aggressive conditions,except those situated in coastal area.

ii) Moderate

Concrete surfaces sheltered from severe rain or freezing

whilst wet.Concrete exposed to condensation and rain.Concrete continuously under water.

Concrete in contact or buried under non-aggressivesoil/ground water.soil/ground water.

Concrete surfaces sheltered from saturated salt air incoastal area.

iii) Severe

Concrete surfaces exposed to severe rain, alternate

wetting and drying or occasional freezing whilst wet orsevere condensation.Concrete completely immersed in sea water.

Concrete exposed to coastal environment.

iv) Very Severe

Concrete exposed to sea water spray, corrosive fumes or

severe freezing conditions whilst wet.Concrete in contact with or buried under aggressivesub-soil/ground water.

v) ExtremeSurface of members in tidal zone.

Members in direct contact with liquid/solid aggressivechemicals.

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Step-5. Selection of Water ContentSelection of water content depends upon a number of factors such as

• Aggregate size, shape & texture

• Workability

• Water cement ratio

• Type of cement and its amount

• Type of admixture and environmental conditions

Factors that can increase water demand

Factors that can reduce water demand are

as follows

•Using increased aggregate size

•Reducing water cement ratio

•Reducing the slump requirement

•Using rounded aggregate

•Using water reducing admixture

Factors that can increase water demand

are as follows

•Increased temp. at site

•Increased cement content

•Increased slump

•Increased water cement ratio

•Increased aggregate angularity

•Decrease in proportion of the coarse

aggregate to fine aggregatePatil Hitesh S

Select the water content per cubic meter ofconcrete from table2 of IS: 10262-2009.

Maximum size of

Aggregate(mm)

Water Content per

cubic meter of concrete

(Kg)

10 208

20 18620 186

40 165

For M35 i.e medium grade

•The values given in the table shown above is applicable only for angular coarse aggregate and for a slump value in between 25 to 50mm

•W/C = 0.6, workability =0.80 Compaction factor, slump = 30mm approx

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Maximum size of

Aggregate(mm)

Water Content per

cubic meter of concrete

(Kg)

10 200

20 18620 186

For grade above M35 i.e. Higher Grade concrete

•The values given in the table shown above is applicable only for angular coarse aggregate and for a slump value in between 25 to 50mm

•W/C = 0.35, workability =0.80 Compaction factor, slump = 30mm approx

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Type of material/condition Adjustment required

1. For sub angular aggregate ------------------Reduce the selected value by 10kg

2. For gravel with crushed stone --------------Reduce the selected value by 20kg

3. For rounded gravel---------------------------- Reduce the selected value by 25kg

4. For every addition of 25mm slump --------Increase the selected value by 3%

5. If using plasticizer ------------------------------Decrease the selected value by 5-10%

6. If using super plasticizer ---------------------Decrease the selected value by 20-30%

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6. If using super plasticizer ---------------------Decrease the selected value by 20-30%

Note: Aggregates should be used in saturated surface dry condition. While

computing the requirement of mixing water, allowance shall be made for the free

surface moisture contributed by the fine and coarse aggregates. On the other

hand, if the aggregate are completely dry, the amount of mixing water should be

increased by an amount equal to moisture likely to be absorbed by the

aggregate

Step-6. Calculating Cementious Material Content

• Water / Cement is known from step 4

• Water Content is known from step 5

• From these we can find Cement Content

• From table instep 4 see minimum cement content

• The greater of the two values is then adopted.

If any mineral admixture (such as fly ash) is to be used, then

decide the percentage of mineral admixture to be used based

on project requirement and quality of material.

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Volume of Coarse Aggregate per Unit Volume of Total Aggregate

(Table 3, IS:10262-2009)

Maximum

Size of

Aggregate

Volume of Coarse Aggregate per Unit

Volume of Total Aggregate

Zone IV Zone III Zone II Zone I

Step-7. Finding out volume proportions for Coarse aggregate & fine aggregate

Aggregate

(mm)

10 0.50 0.48 0.46 0.44

20 0.66 0.64 0.62 0.60

40 0.75 0.73 0.71 0.69

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The values given in the table shown above is applicable only for a water-cement ratio of 0.5 and based on aggregates in saturated surface drycondition.

If water-cement ratio other than 0.5 is to be used then apply correctionusing the rule given below.

Rule:

1)

0.05 increase in W/C ratio 0.05 decrease in W/C ratio

Decrease CA volume by Increase CA volume by 1)

2) For pump Concrete reduce coarse aggregate content up to 10 %

From this we know volume of CA.

Volume of FA = 1- Volume of CA

0.01 0.01

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Step-8. Mix Calculations

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Step-9. Trial Mix

Conduct a trial mix as per the amount of material calculated above.

Step-10. Measurement of Workability (by slump cone method)

The workability of the trial mix no.1 shall be measured. The mix shall becarefully observed for freedom from segregation and bleeding and itsfinishing properties.

Step-11. Repeating Trial Mixes

If the measured workability of trial mix no.1 is different from stipulated value, thewater and/or admixture content shall be adjusted suitably. With thisadjustment, the mix proportion shall be recalculated keeping the free water-adjustment, the mix proportion shall be recalculated keeping the free water-cement ratio at pre-selected value.

Trial-2 – increase water or admixture, keeping water-cement ratio constant

Trial-3-Keep water content same as trial-2, but increase water-cement ratio by10%.

Trial-4- Keep water content same as trial-2, but decrease water-cement ratio by10%

Trial mix no 2 to 4 normally provides sufficient information, including therelationship between compressive strength and water-cement ratio.

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• Cast atleast 3 cubes for each trial mix.

• Test the cubes for compressive strength at 28 days.

• Draw a graph between compressive strength Vs C/W Ratio.

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